1. Field of the Invention
The present invention relates to an iron base Si--Mn alloy or an iron base Si--Mn--Ni alloy, particularly having good crushability and alloy powder thereof.
2. Description of the Prior Art
Ferromanganese, ferrosilicon, and silicon-manganese which have been conventionally used mainly as a deoxidizing agent, a desulphurizing agent, a slagging agent and an alloying component addition agent when iron and steel are manufactured, as stipulated in the Japanese Industrial Standard (hereinafter referred to as JIS") (G2301, G2302, G2304--1986), contain large amounts of alloying components (for example, Mn.gtoreq.73%, (Mn+Si).gtoreq.74%) and also have an extremely high carbon content (for example, FMnM2: C.ltoreq.2.0%, SiMnO: C.ltoreq.1.5%). And these ferroalloys are usually supplied as alloy powder or alloy particle according to a particle size stipulated for use. That is to say, these ferroalloys, as shown in a method for making a lot in JIS, have a feature in the properties thereof that they are supplied in large quantity and in powder form or in particle form, which is realized by the fact that they have the high contents of alloying components and carbon and that they are easily made into powder form or particle form after they are molt en and cooled. On the other hand, in recent years, as the variety of steel products has been increased, there have been more demanded ferroalloys in powder form which have the lower contents of Si, Mn and C than those stipulated in the JIS. For example, the flux of a flux cored wire for arc welding applied to the welding of a steel structure contains various kinds of powder materials such as a slagging agent, a deoxidizing agent, an alloying addition agent, iron powder and the like according to the object and, to be more specific, it contains dozens % total of above described ferromanganese, ferrosilicon, and silicon-manganese in powder form and iron powder. The segregation of the components caused by these mixed flux has a bad effect on the quality of the welded steel products in some cases.
Therefore, it is strongly desired that the simple ferroalloy powder having the same composition as the composition made by blending some kinds of powder materials described above is made in advance and used for the flux. But, in general, as the contents of Si, Mn and C are reduced in a ferroalloy, the ductility and the toughness of the ferroalloy are gradually improved and thus it is difficult to manufacture a product in powder or particle form by using conventional manufacturing equipment. If the composition of the ferroalloy is adjusted so as to solve the problems, the ferroalloy powder is apt to bear magnetism. When a flux cored wire is manufactured, for example, by using the flux mixed with the ferroalloy powder bearing magnetism and by continuously forming a steel strip, filling the flux and performing seam welding as proposed in Japanese Examined Patent Publication No. 4-72640, the segregation of the components and incomplete fusion in the seamed portion and the like might occur in some manufacturing conditions and thus have a bad effect on the manufacturing yield of the flux cored wire and the quality of the welded steel products. Moreover, for example, the flux of the flux cored wire for arc welding applied to the welding of a steel structure made of high-tensile steel or low-temperature steel usually contains Si, Mn, Ni, iron powder and the like together. The above described ferrosilicon, ferromanganese, silicon-manganese, ferronickel in powder or particle form and the like are mainly used as these raw materials in addition to simple raw materials (Si powder, Mn powder and Ni powder). These alloying components of Si, Mn, and Ni strongly react with each other to decrease the quality of the welded part. Therefore, it is desirable that the flux blended and mixed with the raw materials does not have the segregation of components which is apt to be caused by the lot-by-lot compositional variations of the raw materials and the kind-by-kind difference in particle diameter of the raw materials and that the flux has a flux composition containing the predetermined amounts of Si, Mn and Ni. As a result, this requires simple iron base Si--Mn alloy powder containing Ni.